Effect of Natural Standing and Rest on Solute Transport Pathways in Hypermobile and Immobile Human Lumbar Intervertebral Discs. Results from Delayed Post-Contrast Upright MRI Study

Abstract Purpose To examine how physiological states of resting and standing effect the nutrient transport in mobile, hypermobile and immobile lumbar intervertebral discs. Methods This prospective study included 15 healthy participants (10 males, 5 females; mean age, 25.2 ± 3.6 years), divided into three groups: normally mobile, hypermobile (bilateral L5 pars defects), and immobile (lumbosacral transitional vertebrae), with five participants per group. Six-hour delayed post-contrast (0.3mmol/kg) T1-weighted MR images were obtained using a 0.25-T upright positional MRI system in supine, standing, and immediate post-standing recovery positions. Three-dimensional segmentation using 3D Slicer enabled regional enhancement analysis of the central nucleus pulposus (CNP), peripheral nucleus pulposus (PNP), and superior and inferior endplate zones. Results Normal discs showed standing-associated enhancement loss (wash-out) in both CNP and PNP, followed by recovery, particularly peripherally. Hypermobile discs demonstrated the largest standing-associated reduction in CNP enhancement of approximately 2.8 times that of normal discs, with incomplete regain in recovery position. Immobile discs demonstrated the greatest peripheral enhancement loss and limited central recovery. Their superior endplate exhibited a marked, reversible enhancement increase during standing, while the inferior endplate showed comparatively little positional variation. Conclusions For the first time, present study documented acute effects of natural standing and rest on solute transport of human lumbar discs with different mobility patterns in vivo. Despite similar morphology, discs at hypermobile and immobile segments demonstrated different patterns of enhancement wash-out on standing as well as different recovery patterns during rest.